Red Bull Racing team boss Christian Horner says the 2012 Formula 1 title chase pushed his staff harder than they had ever been pushed before.
Sebastian Vettel and Red Bull ultimately delivered their third consecutive world championship double, but only after overcoming Fernando Alonso in a battle that remained on a knife edge until the final laps of the season.
Earlier in the year Red Bull had often appeared to be on the back foot as McLaren enjoyed periods of dominance and teams like Lotus and Mercedes appeared at the front.
"They've always worked hard but this year I think by far has been our toughest challenge," Horner said of his staff.
"It's been the hardest championship, constructors and drivers, because we've had to really fight our way back into them; that is what made it the most gratifying in many respects."
Click here for AUTOSPORT's video guide to Red Bull's final round of key upgrades
Horner underlined that 2012 had seen Red Bull personnel go 'beyond the call of duty' more than ever before.
"The personal sacrifices the time that's given up away from home away from family and friends, particularly in Milton Keynes has been just remarkable," he said.
"The reason this team is so successful is because of the spirit within the team. The way that we work as a team, the way that we work as one unit.
"There's so many heroic stories this year of people going beyond what they are asked of to deliver, to get performance from the car, to get components to the circuit, to get development into the windtunnel, to hit all of those targets.
"What you see on a Sunday afternoon is a very small percentage of what is involved in a grand prix team. This championship, and a triple championship, would never have been imaginable without the commitment of the staff."
Click here for AUTOSPORT's full 2012 Formula 1 season review